The Tremec TKO five-speed transmission is one of the most versatile aftermarket replacement gearboxes available. The TKO was designed to replace a great number of 3, 4, and 5 speed manual transmissions with a 600 lb-ft of torque rating. The flexibility of this unit makes installation possible in any number of older vehicles and almost any variety of hot rods. Fifth gear in the TKO is available in two overdrive ratios, making it much more fuel efficient than the older 3 and 4 speeds it can replace. The low deck height of the transmission case makes it very versatile in fitting to older car models without altering the floor pan or tunnel. The TKO is equipped with both electronic and gear-driven speedometer drives, has multiple shifter locations available, and can mount to most available bellhousings without fabrication. It is available with several different ratios, which can be tailored to keep many power plants in the power band with good fuel economy. The input shaft spline count is 26 and the output spline count is 31, which gives the installer a vast number of clutch and prop shaft choices. There is a TKO500 model available that has 500 lb/ft of torque rating and comes with a 10 spline input shaft.

Tremec is a multinational transmission and gear manufacturer with manufacturing based in Mexico. Most of the three- and four-speed transmissions Ford has used over the last 60 years were designed and manufactured by Tremec, including the four-speed Top Loader. Several years ago, Tremec acquired the transmission business line from Borg Warner, which gave Tremec the T5 and T56 units. The T5 had an extremely long and large model run, being found in Ford, GM, Jeep and Nissan, but was not capable of surviving the horsepower wars that were on the horizon. The strongest T5 model was rated at 330 lb/ft of torque. At this point GM went to the T56 for the F body cars and Corvettes, which gave them a 6 speed with double overdrives and a much higher torque rating. Tremec than created the 3550 transmission, a five-speed rated at 350 to 375 lb-ft of torque with an overdriven fifth gear. It replaced the T5 in Mustangs. Still seeking more torque capacity, Tremec revised the 3550 to become the current TKO. In the process, they modified the 3550’s one-position shifter to a dual shifter location, making installation in a variety of vehicles easier. The engineers then added both mechanical and electronic speedometer drive gears on the main shaft so the unit would work with both early and late models of vehicles. The case mounting flange had a bolt pattern that would work on the stock bellhousings of many cars originally equipped with three- or four-speed transmissions. With the TKO, a whole aftermarket industry sprang up where vendors would sell a TKO with a kit for easy install in many previous models. These kits include cross members, mounts, drive shafts, speedometer cables, etc. to make it one stop shopping for an easier swap to earlier model cars and hot rods.

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Making a race ready TKO involves strengthening certain components within the transmission, and Rockland Standard Gear are specialists in this area. RSG calls the max-performance versions of the TKO and T56 “Tranzilla”, a name that cleverly conveys the amount of power these things can handle.

So what differentiates a TKO Tranzilla from its stock counterpart? RSG’s president, Michael Weinberg, says the main focus is on the synchronizers. “The principal problem with the TKO is in the synchronizer rings. The stock brass ring is the same ring that was used in the original Top Loader transmissions. This works well for low rpm shifts, but will start to block out shifts at engine speeds higher than 5,000 rpm. [Rockland Standard Gear] engineered and manufactures carbon-fiber-lined synchro rings that will shift at 8,000 rpm all day long.” While 8,000 rpm may seem excessive, consider that LS, new Hemi, and especially Coyote engines will easily exceed 5,000 rpm in bone-stock applications, so the need is there for better shifting at high rpm.

When re-assembling the transmission, Weinberg stresses the importance of main- and countershaft endplay tolerances. “There is nothing wrong with the factory product, but an assembly line can never hold the tolerances that an experienced craftsman can on a custom build. We assemble each unit to zero the endplay at the shafts. Endplay is the axial or back and forth play of the shafts when supported in the case by the tapered roller bearings of the design. You need zero endplay and zero preload on the shafts.” RSG’s builders achieve zero endplay by stacking precisely machined shims in the case until there is no back and forth movement of the shafts. Zero preload implies that the shafts turn with no more drag than the bearings and gear train produces. If the endplay is too tight with a measureable preload, you will wipe the oil film off the bearings. Too much endplay will have the shafts moving back and forth as the helical cut gears try and walk away from each other under acceleration. This causes premature wear on the bearings and can also contribute to other problems such as jumping out of gear.

It’s important to remember that endplay will change as the transmission comes up to operating temperature. The aluminum case expands more rapidly that the steel components inside it, so in the car at normal operating conditions, you wind up with 0.002-inch endplay, which is excellent. Another area that demands attention is the counter shaft front bearing retainer. This steel retainer holds the front countershaft tapered roller bearing race or cup in place and is subject to leaks. The retainer fits very precisely into the transmission case and is sealed with a rubber o-ring fitted to a groove machined in the retainer. Always install a new o-ring and put a thin film of RTV silicone around the ring before installing in the case. The dimensional fit is extremely close and it is very easy to shave a piece off the o-ring during installation, resulting in a nasty, slow leak.

The next part that receives attention is the shift finger- a lug that is attached to the shifter rail with a spring pin. It moves the shift forks into position during gear selection. From the factory, the shift finger has two 45-degree chamfers machined in it. During a rapid 2-3 shift, the chamfer can inadvertently guide the finger to get between the shift rails, resulting in a missed shift. Rockland Standard Gear removes the chamfer and eliminating the possibility of a missed 2-3 shift.

With the modifications completed and all covers in place, the transmission is filled with lube and sent to the dyno for the final testing, where it is checked for proper shifts, noise, and smooth up and downshifts. The transmission is also pressurized with low-pressure air to make sure that there are no leaks.

“Tremec builds a great unit, we are simply correcting some problems to make it better at high rpms and blue printing the assembly to the tightest tolerances possible,” Weinberg explains. He also stresses the importance of properly breaking in the transmission, which would ideally be 500 miles of city driving over several days, using all the gears at light and medium throttle, gradually working up to near full-throttle runs through each gear. Be extremely careful with clutch adjustment to make sure that you have a proper release during shifts. The number one cause of early transmission failure, beyond lack of lube, is a misadjusted clutch with too much air gap between the release bearing and the clutch diaphragm fingers. If the clutch cannot fully release, disconnecting the engine from the transmission while shifting, all of the torque and momentum of the vehicle will bear down on the small surface area of the synchro ring, which was never designed to handle those forces. The synchronizer sliding sleeve and the engagement teeth of the speed gears will also get damaged, and those repairs are expensive. Remember if the clutch slips on engagement you only hurt the clutch, but a clutch that does not have sufficient release destroys the transmission in short order.

The stock, brass synchronizers in the TKO five-speed weren’t designed for high-rpm shifting. For applications where engine speeds routinely exceed 5,000 rpm, Rockland Standard Gear replaces the brass rings with these carbon-fiber lined rings which have been tested to shift at engine speeds up to 8,000 rpm.One of the components that can contribute to missed shifts at high rpm is the shift finger. On a rushed second to third gear shift, it can guide itself between the shift rails without actuating the third gear shift fork.To build a Tranzilla TKO, Rockland Standard Gear replaces the stock shift finger with their own design (right) that is not chamfered and cannot slip between the shift rails.The front countershaft bearing retainer fits precisely in the case. It is sealed with an o-ring that is easily damaged. RSG installs the retainer with a slight amount of silicone sealant and verifies case integrity with compressed air to ensure this seal does not leak.This is the TKO’s fifth speed gear with RSG’s own carbon fiber synchronizer ring installed. Note the needle bearings, which ride on a sleeve over the main shaft. Care must be taken with disassembling and reassembling the transmission to avoid scattering the rollers.RSG modifies so many TKOs they’ve made a tool out of used parts that helps them replace the 5th gear synchronizer ring without having to remove the roller bearing assembly.This picture shows the tool being used to press out the Fifth Gear sleeve, leaving the roller bearing intact.Here are several new carbon-fiber-lined synchronizer rings soaking in lube prior to assembly in a TKO Tranzilla.Here is the TKO’s main shaft prior to disassembly. RSG Will replace the brass synchronizer rings with new carbon-fiber-lined rings.Because the TKO transmission was designed to be an aftermarket replacement for a number of OE units, it has provisions for both electronic and cable-driven speedometers. That’s a tone wheel for an electronic speedo next to the nylon gear for a cable driven speedo.This picture shows the thin line of silicone sealant applied to the front bearing retainer. The o-ring can be damaged during installation, and the silicone helps mitigate any leaks in case it does.With the shifter removed, you can see the two mouting positions for the shifter on the main shift rail. The four-bolt steel cover next to it reveals a “mid-shift” location that is also possible.Rebuild complete, this Tranzilla-converted TKO is ready to ship. Note that the shifter is mounted in the farthest rearward position. Between the three optional shifter locations in the TKO and the myriad of shifter handles available, it’s possible to mount a TKO in nearly any car’s original console. If you like the idea of a race-ready, high-rpm five-speed, there are several options. You can buy a Tranzilla TKO outright from RSG, or you can send them your stock TKO to be converted to Tranzilla specs.